1. Field of the Invention
The present invention relates to a connector which is used in an electronic device having a plurality of circuit boards, and which electrically connects one of the circuit boards to another. In particular, the invention relates to an arrangement of contacts for use in the connector, and a structure of each contact.
2. Description of the Related Art
With developments in functions of electronic devices and with higher complexity of electronic devices, connectors each having many contact portions have been developed in order to interconnect many electrical wiring lines. In the case of the connector for use in, e.g. an artificial satellite, it is very difficult to repair or replace the connector after the artificial satellite is launched. Thus, high reliability is required in the connector as well as in the electronic devices which are mounted.
The electric connector that is used in the electronic device requiring high reliability may adopt various structures. For example, as regards a signal that is transmitted with use of the electric connector, if a fault occurs in one signal path, it is necessary to protect the signal that is transmitted. For this purpose, one method may be used in which the same signal is distributed to some other electrodes, thereby to secure the signal. However, the structure in which one signal is distributed to several electrodes increases the number of electrodes of the connector to be used, and also increases the fabrication cost. The method that provides such redundancy makes the wiring and the circuit itself complex. It is not practical to adopt such a method in all devices which are mounted.
Defective contact of a contact portion is a major factor of the defectiveness of the connector. In many cases, defective contact occurs due to resilient fatigue of the contact member itself, and contamination or damage of the surface of an associated electrode.
To solve this problem, a structure shown in FIG. 7, for instance, may be adopted. In this structure, a contact 70 is formed of a single metallic resilient member 71 for transmitting one signal. A distal end portion of the contact 70, which comes in contact with an associated electrode 72, is divided into two resilient contact arms 73, thereby effecting two-point contact. A method using this structure is adopted in order to cope with occurrence of defective contact. However, even in the case where the distal end portion of one contact is divided into two parts to effect two-point contact, as shown in FIG. 7, the proximal portion of the contact is a single part. Thus, if a problem occurs in the part other than the part that comes in contact with the associated electrode, there is no measure to cope with such a problem. In addition, in the structure shown in FIG. 7, there are some cases in which a uniform and sufficient contact pressure can hardly be secured.
Another method is shown in an exploded view of FIG. 8A to FIG. 8G, for instance. In this method, a silicone rubber connector 75 is used. In this silicone rubber connector 75, an electrically conductive sheet 79 as shown in part of FIG. 8B is used as a signal transmission member 78 which is interposed between upper and lower wiring boards 76 and 77 as shown in parts of FIG. 8A and FIG. 8D. As shown in parts of FIG. 8E and FIG. 8F, the electrically conductive sheet 79 can be formed by aligning, with high density, electrically conductive fibers 81 or electrically conductive rubber, or metallic particles, in a sheet-like member formed of insulative silicone rubber. A frame 83 shown in part of FIG. 8C has an inner wall 84. The inner wall 84 is located around the signal transmission member 78, for example, for the purpose of positioning of the signal transmission member 78 and structural reinforcement of the silicone rubber connector 75.
Part of FIG. 8E is a top view, and part of FIG. 8F is a cross-sectional view taken along line X-X′ in part of FIG. 8E. As shown in parts of FIG. 8E and FIG. 8F, electrically conductive fibers 81, for instance, vertically extend, and accordingly an electric current flows only in the vertical direction. Part of FIG. 8G shows a contact state between the electrically conductive fibers 81 and contacts 85 of the wiring board. The resistance value of the connection part is determined by the number of electrically conductive fibers 81 per contact 85. By virtue of this structure, only the associated contacts 85 and 86 can surely be electrically connected in the stacked state in which the electrically conductive sheet 79 is disposed between the upper and lower wiring substrates 76 and 77.
In the silicone rubber connector, in particular, in the case where high reliability is required as in use for an artificial satellite, gold wires are buried, in typical cases, as the electrically conductive fibers 81, thereby to ensure the reliability. As regards the silicone rubber connector in which expensive gold wires are buried, such other problems arise that after the connector is once used, the connector cannot be recovered and used.
In addition, if a great load is applied to the silicone rubber connector, the silicone rubber connector cannot be re-used. Besides, with use of metal wires with excessively small diameters, it is difficult to increase a transfer speed by increasing the frequency of a signal that is transmitted.
An example of patent documents relating to connectors is Jpn. Pat. Appln. KOKAI Publication No. 2002-190335.